Separation of molybdenum values from tungsten values by solvent extraction

ABSTRACT

A process for the recovery of molybdenum values from a concentrated mineral acid solution that also contains tungsten as a contaminant is disclosed. The process comprises contacting an acid solution that has a mineral acid concentration of at least one normal acid solution with an organic extractant phase consisting essentially of monohexadecyl phosphoric acid and a water-insoluble hydrocarbon, as a solvent, to extract at least a portion of the molybdenum from the acid, separating the molybdenum-pregnant organic phase and the spent acid solution, thereafter contacting the molybdenum-pregnant organic solution with an aqueous strip solution containing a source of ammonium ions to remove at least a portion of the molybdenum from the organic phase, separating the resulting ammonium molybdate strip solution from the molybdenum-barren organic phase and recovering said strip solution as a solution of ammonium molybdate that is essentially free of tungsten.

United States Patent [73] Assignee [54] SEPARATION OF MOLYBDENUM VALUES FROM TUNGSTEN VALUES BY SOLVENT EXTRACTION 6 Claims, No Drawings [52] U.S. CI 23/22, 23/23, 23/51, 23/140, 23/15 W, 23/312 ME [51] Int. Cl C22b 59/00, C01 g 39/00 [50] FieldoiSearch 23/15,5, 18-20, 22-24, 51, 312 ME [56] References Cited UNITED STATES PATENTS 2,860,031 11/1958 Grinstead 23/23 X FOREIGN PATENTS 967,823 8/1964 Great Britain Attorneys-Norman .I. OMalley, Donald R. Castle and William H. McNeill ABSTRACT: A process for the recovery of molybdenum values from a concentrated mineral acid solution that also contains tungsten as a contaminant is disclosed. The process comprises contacting an acid solution that has a mineral acid concentration of at least one normal acid solution with an organic extractant phase consisting essentially of monohexadecyl phosphoric acid and a water-insoluble hydrocarbon, as a solvent, to extract at least a portion of the molybdenum from the acid, separating the molybdenum-pregnant organic phase and the spent acid solution, thereafter contacting the molybdenum-pregnant organic solution with an aqueous strip solution containing a source of ammonium ions to remove at least a portion of the molybdenum from the organic phase, separating the resulting ammonium molybdate strip solution from the I molybdenum-barren organic phase and recovering said strip solution as a solution of ammonium molybdate that is essentially free of tungsten.

SEPARATION OFMOLYBDENUM VALUES FROM TUNGSTEN VALUES BY SOLVENT EXTRACTION BACKGROUND OF THE INVENTION This invention relates to a new method for reclaiming molybdenum from concentrated mineral acid solutions. More particularly, it relates to a liquid-liquid solvent extraction process whereby tungsten-free molybdenum is recovered from an acidic molybdenum solution by transfer to an organic extractant and followed by recovery of molybdenum values as aqueous ammoniacal molybdate solutions suitable for further processing by conventional methods.

Molybdenum mandrels are used in the production of tungsten wire products, coils and the like. After processing of the wire products, the mandrels contaminated with tungsten, are generally dissolved in an acidic etch solution consisting of, for example, 30 vol. nitric acid, 30 vol. sulfuric acid, and 40 vol. water. The mandrel etch solution typically contains l5% molybdenum and 25% tungsten, as an impurity. Heretofore, the solution was sewered. Currently, some form of reclamation is necessary to reduce water pollution. One method to achieve the reclamation is by the neutralization of the solution with ammonium hydroxide and recovering the molybdenum values by a method hereinafter given. For example, the addition of ammonium hydroxide to neutralize the etch solution at 1 C. yields, upon cooling to C., a solid mixture of ammonium sulfate, ammonium paramolybdate, and ammonium nitrate. Subsequent firing of the material at 500 C. to convert the ammonium paramolybdate to molybdenum trioxide (M00 and to volatilize the sulfate and nitrate which are present, yields a product (M00 that contains up to about 5% by weight of tungsten.

Some of the disadvantages'of this method are readily apparent, as for example, theamount of NH OH necessary to neutralize the acidic solution is excessive because a mole of NH,OH is required for each mole of acid. The addition of the large quantities of NH,OH further dilutes a very dilute molybdenum-containing starting material. Additionally, tungsten precipitates with the molybdenum and further processing or purification steps are necessary to generate a relatively pure molybdenum product that is required for metallurgical applications. The product yield is too low to be economically and efficiently geared to production processing. In addition, burning of such large quantities of sulfates and nitrates generates atmospheric pollution problems.

In copending patent applications Ser. No. 837,894 and Ser. No. 837,777 filed concurrently herewith, extraction processes for the recovery of molybdenum from sources that are contaminated with tungsten, such as technical-grade MoO or molybdenum containing ores, are disclosed. In these methods the conversion to sodium or potassium molybdate solutions occurs first, then this product is acidified by a mineral acid to yield a solution having a pH offrom about I to 3.

These methods use specific extractants that will not operate efficiently under conditions employed in the process of the present invention.

It is believed therefore, that a process that would recover molybdenum that is essentially tungsten-free from such acid solutions directly, without pollution problems, would be an advancement in the art.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention there is provided a process wherein the before-mentioned concentrated molybdenum-containing acid solution is contacted with a water-insoluble extractant solution consisting essentially of monohexadecyl phosphoric acid (MHDPA) and a hydrocarbon solvent for a period of time sufficient to extract at least a portion of the molybdenum values from said concentrated acid, separating the spent acid solution and the resultant molybdenum-pregnant organic solution, contacting said organic solution with an aqueous strip solution containing ammonium ions to remove the molybdenum values from the organic solution; separating the organic and strip solutions and recovering said strip solution containing ammonium molybdate. Optionally, the organic extractant solution can be recycled.

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above description of one of the aspects of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention yields a method to recover tungstenfree molybdenum from molybdenum-containing waste acid solutions that are contaminated with as much as 5% tungsten. The efficiency of recovery is generally greater than about 99% by using the solvent extraction technique of this invention.

The finding that tungsten-contaminated molybdenum, dissolved in an H SO,,-HNO solution, can be essentially quantitatively and selectively extracted from such stronglyacid solutions by monohexadecyl phosphoric acid in hydrocarbon diluent is believed to be surprising and unexpected. Numerous attempts to effect separation of molybdenum and tungsten under highly acid conditions have not, heretofore, been successful, probably because the specie of molybdenum-containing ions are believed to varyv considerably depending upon the pH or acid concentration. Subsequent stripping of the molybdenum-loaded organic extractant by ammoniacal solutions results in the production of tungsten-free ammonium molybdate solution. Such solutions are further processable by normal methods suchas crystallization, spray drying, kettle drying, firing, etc., to produce ammonium paramolybdate, ammonium polymolybdate, molybdenum trioxide, etc.

Alternatively, molybdenum scrap, such as floor sweepings, wire, sheets, etc. Can be added to the acid solution before processing. When available, the foregoing addition of otherwise waste materials yields additional benefits. For example, the concentration of molybdenum in the acidic solution is increased and the economics of the system are thereby improved. Additionally, the scrap molybdenum can be efficiently processed and recovered.

Generally, the concentration of molybdenum in the aqueous feed solution can vary from about 10% to about 60% by weight, depending on the amount of scrap molybdenum that is dissolved in acid solution. Low levels, that is below 10% do not effect the extraction of stripping capabilities or the recovery, however do lower the capacity of the system. A feed solution of greater than 10% concentration is preferred from a capacity and equipment investment viewpoint on the basis of cost per unit of MoO processed. The molybdenum-containing acid solutions that are about 15 to 16 N upon the digestion of the molybdenum, can be diluted to any normality, but normalities of greater than I are preferred and normalities of from about 4 to about 10 are especially preferred since the higher molybdenum concentrations achieve more efficient results. Extreme dilution so that the pH of the solution is above about 0.5 is to be avoided since other nonextractable molybdenum species can occur.

The volume ratio of extractant to solvent can vary from about 5.95 to about :5, but a ratio of from about 10:80 to about 10:90 is preferred. Ratios outside the foregoing range of from about 5:95 to about 95:5 result in either poor efficiency and increased stages or are unnecessary and uneconomical. Although the hydrocarbon can be any water-insoluble hydrocarbon solvent such as the petroleum distillate solvents such as kerosene, toluene, benzene, naptha and the like, kerosene is preferred because of its cost, flash point and toxicity rating. The volumetric phase ratio of the organic extractant phase to aqueous acid solution can vary from about 6: l to about 116, but ratios of from about 4:1 to about 6:1 are preferred.

The optimum number of extraction stages can vary depending upon the concentration of the acidic solution. For exam- 3 4 ple, the optimum number of extraction stages is four when a Sample Normality 61 Organic /3 10 N acid solution is contacted with organic solution in a 4 to Add 1 organic to aqueous (o/a) ratio. Underthese conditions an efficiency greater than about 99.5% is achieved. An efficiency l 6 [0% MHDPAH mm 619 of 98% is obtained when only three extraction stages are used 2 7 MHDPAH M72 675 under similar conditions. The number of stripping stages can 3 a 10% MHDPAZ-l 0.768 66.5 also vary, generally from 1 to 3, depending on the efficiency 4 9 MHDPAZ-I level and the stripping agent used. 2 2 :8: $33523: 81 33% The time required for contacting the acid feed solution with 1 7 7 10% 0:775 the organic extractant solution can be varied, however, a time 10 a s 10% MHDPM-l 0.101 13.8 period from about 5 to about minutes is preferred in order 9 9 10% MHDPM to achieve the best efficiency and throughput. MHDPM The ammoniacal stripping agents can be ammonium oxalates, eitrates, hydroxides, or chlorides but about a 1N NH,C1 l5 EXAMPLE 11 or about a 1 IN NH OH stripping agent is preferred because of cost, efficiency, added impurities, ease of handling, and finished product obtained. Ammonium chloride can be used as a stripping agent, however, its use would depend upon whether or not the presence of chloride ions would be detrimental to the end use of the subsequently produced ammonium molybdate.

The time necessary to achieve removal of molybdenum from the organic solution by the stripping agent can be varied, however, at least about 5 minutes is necessary for good efficiency, that is greater than about 90%. A contact time greater than about 25 minutes is not necessary and needlessly prolongs the overall time cycle.

To more fully illustrate the invention, the following detailed nonlimiting examples are presented. All parts, ratios, proportions and percentages are by volume unless otherwise indicated.

A similar extractant solution, as in Example 1, is contacted with acidic molybdenum-containing solutions, diluted to 4 N and in a 1:1, o/a ratio, for times ranging from 1 minute to 40 minutes. A contact time of 5 minutes is found to be adequate 20 for extraction as is shown by the results of analysis of samples presented below.

Extraction Coefficient Sample Time Minutes Kd war-1N- f EXAMPLE 111 EXAMPLE I 1. An extractant solution containing about 10% MHDPA90% kerosene, containing about 85% by weight of molybdenum, is

{ contactedwith various suitable stripping agents. Results ap- An extractant solution containing about 10% monohexadecyl phosphoric acid (Ml-IDPA) using kerosene as a solvent, is used to contact (in a 1:1 organic to aqueous ratio) a pear below, waste, acidic molybdenum solution (15 N acid solution com- 1 prised of 75% HNO 25% H 80 in which about 15% by S M l w tripping oy cnum weight of molybdenum and about 3% by weight of tungsten 40 smpping Age", organic Cocmcicm snipped are dissolved. Samples of the solution are diluted with deionized water from 14 N to l N and the period of contact is o 5 N NH Cl Mmwmainins 0 09 8 2 for 25 minutes on each sample. Analysis of the samples yield MHDPA the following results: 1.0 N Ni1,c1 Mo-contflinirig 11.02 91.6

MHDPA 3.0 N NH,C1 Mo-containing 0.19 15.9 MHDPA v 2.0 N NH, citrate Mo-cnntaining 0.671 40.1 Sample Normality of Concentration Molyb- MHDPA dcnum 5.0 N NH cit at- Mo-coniainin 0.835 45.5 Molybdenum Acid Organic Kd (11a 4 r L MHDPK g j 2.0 N NH, 6111101: Mo-containing 0.901 41.5 S I r E I MHDPA 0.5 N N11, oxalate Mo-containing 0.531 34.6

MHDPA I i 10% MHDPA 5.29 114.1 11.1 N NH, on Mo-containing 182.54 09.4 2 2 10% Mi-lpPA 5.01 83.3 MHDPA 3 a 10% MHDPA 5.13 115.2 4 4 10% MHDPA 5.84 85.3 6 gi t 2%,; 2;; 1 The above data indicates an improvement in stripping 1s 7 7 10% MHDPA 090 475 achieved when about a 1 N ammonium chloride or about an s a 10% MHDPA 0.12 41.8 1 l N ammonium hydroxide is used as a stripping agent. The :8: $233 3'2; 33': other stripping containing ammonium ions can be used, how- H 70% MHDPA 5,; ever, more stripping stages are required to achieve a high level 12 12 10% MHDPA 0.52 34.2 of recovery. is 13 10% MHDPA 0.66 39.1

l4 14 10% MHDPA 0.50 33.3 EXAMPLE w 15 full strength 10% MHDPA 0.49 32.8

An acidic molybdenum acid solution, that contains tungsten, is tagged with "W and diluted to normalities ranging from about 1 to about 6. The aqueous solutions are contacted The results indicate that above a concentration of 4 Normal l in a 1:1 ola ratio with about a 10% MHDPA in kerosene for 10 the extraction capability of MHDPA decreased sharply when l minutes. Aliquots of both phases are counted and distribution a 1:1 o/a phase ratio is employed and the efficiency decreases l j coefficients obtained. No counts are detected in the organic some at concentrations less than 4 Normal. However, when hases even through the counts in the aqueous phases were higher o/a ratios are used, the tolerable acid strength or ioni 1 high 5,000 c.p.m.) it can be concluded that MHDPA is concentration is sharply increasedas is shown below. lilective for molybdenum and that tungsten is not extracted.

EXAMPLE v Molybdenum acid solution (15.6 N) is diluted to 4 N with deionized water and contacted with 10% MHDPA in kerosene for 5 minutes in a 1:1 o/a ratio. AFter settling, the aqueous phase is contacted with fresh organic extractant and continued for a third time. After three contacts over about 94.5% of the M is extracted. The organic solutions are combined and contacted with an equal volume of 1.0 N NH CI. After two contacts a 99% tungsten-free molybdenum is stripped.

While there has been shown and described what is at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

We claim:

I. A process for the recovery of molybdenum from a concentrated mineral acid solution containing tungsten, said process comprising:

a. contacting a mineral acid solution having a normality of at least about 1 N, with an organic extractant solution consisting essentially of monohexadecyl phosphoric acid and a water-insoluble hydrocarbon solvent having a volumetric ratio of said acid to solvent of from about 5:95 to about 95:5, the volumetric ratio of said acid solution to said extractant solution being from about 1:6 to about 6:1 to extract at least some of said molybdenum;

b. separating the resultant molybdenum-pregnant organic phase from the resulting aqueous spent acid solution;

c. contacting said organic phase with an aqueous strip solution containing an ammonium ion source to remove at least some of said molybdenum from said organic phase;

cl. separating the resultant molybdenum-barren organic phase and the resultant ammonium molybdate strip solution; and

e. recovering said ammonium molybdate strip solution that is essentially tungsten free.

2. A process according to claim 1 wherein said stripping solution is selected from about 1 N ammonium chloride and about 1 l N ammonium hydroxide.

3. A process according to claim 2 wherein said acid solution is from about 4 N to about IO N.

4. A process according to claim 3 wherein the concentration of molybdenum in said acid solution is greater than about 10% by weight.

5. A process according to claim 2 wherein said molybdenum-barren organic phase is recycled to contact said aqueous mineral acid solution.

6. A process according to claim 5 wherein said process is a continuous process. 

2. A process according to claim 1 wherein said stripping solution is selected from about 1 N ammonium chloride and about 11 N ammonium hydroxide.
 3. A process according to claim 2 wherein said acid solution is from about 4 N to about 10 N.
 4. A process according to claim 3 wherein the concentration of molybdenum in said acid solution is greater than about 10% by weight.
 5. A process according to claim 2 wherein said molybdenum-barren organic phase is recycled to contact said aqueous mineral acid solution.
 6. A process according to claim 5 wherein said process is a continuous process. 